Thou shalt - let the dam go, and take the young to thee; that it may be well with thee - This passage may be understood literally. If they destroyed both young and old, must not the breed soon fail, and would it not in the end be ill with them; and by thus cutting off the means of their continual support, must not their days be shortened on the land? But we may look for a humane precept in this law. The young never knew the sweets of liberty; the dam did: they might be taken and used for any lawful purpose, but the dam must not be brought into a state of captivity. They who can act otherwise must be either very inconsiderate or devoid of feeling; and such persons can never be objects of God's peculiar care and attention, and therefore need not expect that it shall be well with them, or that they shall prolong their days on the earth. Every thing contrary to the spirit of mercy and kindness the ever blessed God has in utter abhorrence. And we should remember a fact, that he who can exercise cruelty towards a sparrow or a wren, will, when circumstances are favorable, be cruel to his fellow creatures. The poet Phocylides has a maxim in his admonitory poem very similar to that in the sacred text: -
Μηδε τις ορυιθας καλιης ἁμα παντας ἑλεσθω·
Μητερα δ' εκπρολιπῃς, ἱν' εχῃς παλι τησδε νεοττους.
Phocyl. Ποιημα Νουθετ., ver. 80.
"Nor from a nest take all the birds away;
The mother spare, she'll breed a future day."

But thou shall in any wise let the dam go, and take the young to thee,.... Or "in letting go, let go", or "in sending, send away" (a); that is, willingly, certainly, entirely, frequently, always; so the Jewish canons (b),"if anyone lets her go, and she returns, even four or five times, he is obliged to let her go, as it is said, "in letting go, let go";''nay, Maimonides says (c), even a thousand times; the canon proceeds,"if anyone says, lo, I take the dam and let go the young, he is obliged to let her go; if he takes the young, and returns them again to the nest, and after that returns the dam to them, he is free from letting her go;"
that it may be well with thee, and that thou mayest prolong thy days; the Targum of Jonathan is,"that it may be well with thee in this world, and thou mayest prolong thy days in the world to come:''the same blessing that is promised to observers of the fifth command, which is one of the weightier matters of the law, is made to this; which the Jews say (d) is but as the value of a farthing, or of little account in comparison of others; wherefore, as Fagius rightly observes (e), God, in bestowing such rewards, has regard not to the works of men, but to his own grace and kindness; for what merit can there be in letting go or preserving the life of a little bird?
(a) "dimittendo dimittes", Pagninus, Montanus, Vatablus; so Ainsworth. (b) Misn. Cholin, c. 12. sect. 3. (c) In Misn. ib. (d) Misn. ib. sect. 5. (e) In loc.

Let the dam go - Partly for the bird's sake, which suffered enough by the loss of its young; for God would not have cruelty exercised towards the brute creatures: and partly for mens sake, to refrain their greediness, that, they should not monopolize all to themselves, but leave the hopes of a future seed for others.